Secondary batteries capable of charge and discharge have been widely used recently as an energy source of wireless mobile devices. In addition, secondary batteries also have attracted an attention as an energy source of electric vehicles, hybrid electric vehicles and the like provided as means for solving air pollution problems of existing gasoline vehicles or diesel vehicles using fossil fuels. Due to many other advantages of secondary batteries, the types of applications using secondary batteries have been widely diversified, and secondary batteries are expected to be used in products from more various fields in the future.
Secondary batteries have different constitutions depending on output and capacity required in the fields and products using such secondary batteries. For example, small mobile devices such as mobile phones, PDAs, digital cameras and lap-top computers use a small battery pack including one, or two, three or four battery cells per one device in order to respond to trends of miniaturization, weight reduction and thinning of the corresponding products. Meanwhile, medium and large size devices such as electric bicycles, electric vehicles or hybrid electric vehicles use a medium and large size battery pack electrically connected to a plurality of battery cells due to the necessity of high output and high capacity. Sizes and weights of a battery pack are directly related to storage space, output and the like of the corresponding medium and large size devices and the like, therefore, manufacturing companies make an effort to prepare a small and light battery pack as possible. Nickel-hydrogen secondary batteries have been most widely used as a battery cell of a battery pack, however, lithium secondary batteries providing high output considering capacity have been extensively studied recently, and some of the lithium secondary batteries have been commercialized.
However, lithium secondary batteries have a fundamental problem of having low stability. Specifically, much heat is generated inside a battery pack when charging and discharging a lithium secondary battery. Among these, much heat is generated in a battery cell, particularly, an electrical region such as an electrode terminal or connector. Moreover, an insulation property is mostly required for an electrode terminal, a connector or the like in the constitution of electrical connection, and in many cases, the electrode terminal or connector is supported on an insulation member, or an insulation member is inserted in a specific structure. Accordingly, heat generated in the electrode terminal or connector is not able to be effectively released, and tends to be accumulated. As a result, deformation occurs in the electrode terminal, the connector or the like and ultimately causes changes in the resistance of a battery pack.
Such changes in the resistance worsen an operating condition and stability of a battery pack, therefore, need to be suppressed. Particularly, heat accumulation may become a serious issue in terms of stability in a medium and large size battery pack using a plurality of battery cells, and in a battery pack using a lithium secondary battery as a battery cell. Accordingly, needs for technologies capable of fundamentally solving such a problem have increased.